Polymeric water-soluble thickening agents are widely known and used in many aqueous systems including latex paints and other aqueous coating compositions.
The widespread use of latex paints, i.e., paints based on aqueous dispersions of synthetic organic polymers, has prompted continued research on product and process improvements. One particularly important concern is controlling the paint rheology to obtain proper flow and leveling with a minimum of dripping and spattering. Cellulose ethers, such as described in Glomski et al. U.S. Pat. No. 3,769,247, are often effectively used as thickeners for latex paints. However solid, water-soluble polymers derived from cellulose and other natural products are becoming increasingly expensive to produce because of high capital, energy, and waste control costs.
Alkali soluble latex copolymers have been known for some time. Thus, Hager and Martin U.S. Pat. Nos. 3,003,987 and 3,070,561 and Miller U.S. Pat. No. 3,081,198 describe copolymers of acrylic and methacrylic acids and esters which may be thickened by replacing a portion of the hydrogen ions of the copolymer carboxyl groups with ammonium or alkali metal ions. Other types of polymeric thickeners are disclosed by Junas and LaTorre U.S. Pat. Nos. 3,652,497 and 3,708,445, Zimmerman U.S. Pat. No. 3,657,175, Chang and McDowell U.S. Pat. No. 3,891,591, and Gibson U.S. Pat. No. 4,003,870. All contain various carboxylic acid groups which can be solubilized in water by neutralization with a water-soluble base. However, to date this technology has had limited impact on major markets for water-soluble polymeric thickeners.
More recently, Evani and Corson developed, as described in U.S. Pat. No. 4,008,202 and related patents, a solid styrene-maleic anhydride-vinylbenzyl ether terpolymer soluble at high pH and useful as a thickener for aqueous solutions. In spite of excellent rheology, stability problems and cost have limited its use as a paint thickener. Further improvements in this technology are clearly desirable.